Method for Power Saving in a Base Station

ABSTRACT

A signal having a frame structure is transmitted and received in a cell by a first base station, the structure of the frame having a downlink frame part and an uplink frame part. Each frame part has the ability of carrying at least one data region allocated to at least one user or broadcasted for the traffic flow between the telecommunication network and the user terminal via the first base station. The downlink frame part has an overhead part with at least synchronization or system information. The frame structured signal is transmitted periodically Frame N, Frame N+1, Frame N+2, Frame N+3 with a normal interval defined by the system. The system during, a power saving mode, increases the interval between at least a first and the next following second frame structured signal to a power saving interval.

TECHNICAL FIELD

The invention relates to a method for energy saving in atelecommunication system according to the preamble of claim 1, atelecommunication system adapted for energy saving according to thepreamble of claim 14 and a node in said telecommunication systemaccording to the preamble of claim 12.

BACKGROUND

Mobile communication is one of the most important technologies forcontributing to social and economic development around the world.Optimizing energy efficiency will not only reduce environmental impact,it will also cut network costs which will give benefits for all usingthe mobile systems.

Modern standards as WCDMA, LTE and WiMAX have very high capacity interms of users and throughput, which requires a large amount of energy.In order to achieve high data throughput in the cellular systems a densecell plan has to be deployed. A base station consumes considerableamount of power, typical 65000 kWh per station and year.

Network design is a key issue improving the energy-efficiency. No amountof energy efficiency at the component level can make up for aninefficiently deigned network. For instance the number of radio sitesshould be optimized for the coverage and quality that needs to beachieved.

In order to achieve an energy-efficient design a number of issues haveto be addressed from start. At first, the true network needs has to beaddressed. The exact coverage, capacity and quality have to beconsidered before getting into considerations about individual sites andequipment specifications. Moreover, the current and future businessenvironment needs has to be considered, considering the possibility torebuild or expand sites. Once these factors have been considered theoperator should begin the network design process, looking into the totalcost of the ownership and the alternative design options.

Capital expenditure typically represents a very small portion of thetotal cost of the ownership. Instead, the long term savings from sitereduction and efficient operation is significant, with a significantreduction in energy consumption as a key issue.

Optimizing solutions for reducing energy consumption means that everystone has to be turned over. Still, the total network solution isgreater than the sum of their parts. This means that combining the bestcomponents in a package does not always give the best results. In theradio base station the relative energy consumption of the differentcomponents vary on the dependency of the properties of the components ithas to work with.

Typical sources of energy consumption in the base station are signalprocessing, RF conversion, power amplification, power supply, climateequipment (air conditioning) and feeder. For instance, In traditionalbase stations the equipment is located on the ground which means thatthe antennas has to be fed using several meters of cable. Half of theemitted power can be lost in the feeders. By placing the equipment inthe top of the tower, significant reductions in energy consumption isachieved. The equipment can be combined with a battery back-up unit thatminimizes hardware and energy consumption.

Another way in which energy reduction can be achieved is through the useof stand-by modes. Base station sites are dimensioned to cope with peakhours. In a cell a number of TRX (transmitters) can run at the sametime. Using power management schemes, some TRX can be put in stand-byinstead of running in idling mode during low traffic hours.

Other ways of reducing the energy consumption is to avoid unnecessaryDC/DC conversion and reduce the need of cooling fans and coolingsystems. Modules based on digital power management can also reduceenergy consumption.

There is an increasing need of delivering wireless technology withbroadband capacity for cellular networks. A good broadband system mustfulfill certain criteria, such as high data rate and capacity, low costper bit, good Quality of Service and greater coverage. High Speed PacketAccess (HSPA) and Mobile WiMAX are examples two network accesstechnologies that enable this. Both of these uses a frame structure forthe uplink and downlink communication between the base station and themobile terminal. In the following part of the background, the technologyof WiMAX will be introduced as an example of a technology using framestructure, but other technologies such as WCDMA, GSM, HSPA and Long TermEvolution (LTE) also use frame structuring. The frames of the differenttechnologies differ to some extent.

WiMAX refers to the IEEE standard 802-16 where Mobile WiMAX relates to802.16e-2005. Mobile WiMAX is an improvement of the modulation schemesused in earlier (fixed) WiMAX standards by the introduction of ScalableOrthogonal Frequency Division Multiple Access (SOFDMA) to carry data andsupporting channel bandwidths with a large number of sub-carriers ondifferent frequencies (sub-channels) within the band. The large numberof sub-carriers improves the performance in multipath fading channels.

Scalable OFDMA is a statistical multiplexing technology, and scalablerefers to the ability of the communication channel to be divided into anumber of variable bit-rate digital channels (sub-carriers) or datastreams. It means a dynamic scheduling wherein a time slot in the accessassigned by the base station can enlarge and contract but still remainassigned to the particular mobile terminal. Different numbers ofsub-carriers can be assigned to different users, and the Quality ofService, i.e. data rate and error probability, can be controlledindividually for each user since the sub-channels are variable. Theband-width of the channel can flex between 1.25 and 20 MHz. OFDMA (onwhich SOFDMA is based) has fixed sub-carrier band-width.

OFDMA is a multi-user version of Orthogonal Frequency DivisionMultiplexing (OFDM) modulation scheme. OFDM is for one single user incontrast to OFDMA. OFDM(A) uses a large number of sub-carriers, in whicheach sub-carrier is modulated for instance with Quadrature AmplitudeModulation (QAM). OFDM has the ability to cope with severe channelconditions, which makes Mobile WiMAX very robust. OFDM also has highspectral efficiency. OFDM may be viewed as using many slowly-modulatednarrowband signals rather than one rapidly-modulated wideband signal.QAM will not be described any further in this document.

The duplex method of Mobile WiMAX is Time Division Duplex (TDD). TDDonly occupies one single channel, with uplink and down link trafficassigned to different time slots. TDD with OFDMA provides subchannelsand time slots enabling multi access for different users. TDD has anadvantage in the case where the asymmetry of the uplink and downlinkdata speed is variable. As the amount of uplink data increases, morebandwidth can dynamically be allocated to that.

The ability of sub-channelling by OFDMA is shown in FIG. 1, which figureillustrates the frame structure schematically. The frame structure asvisualized comprises a number of subchannels and a number of time slots,enabled by OFDMA being a statistical multiplexing technique. The dataregions 11,12,13,14 of the different user devices 11,12,13,14 areillustrated in the figure.

Mobile WiMAX transmitted via base stations uses SOFDMA with TDD. FIG. 2shows a more detailed schematic view of a frame structure for OFDMA whenoperating in TDD mode. The frame (Frame N) comprises a downlink subframe15, a following uplink subframe 16, a small guard interval 20 betweenthe downlink and uplink subframe and an end interval 22 between theuplink and the downlink subframe of the next frame. In mobile WiMAXthese frames are 5 ms long. Some WiMAX systems support OFDMA operatingin Frequency division duplexing (FDD) in which the frame structurediffers from TDD in that the uplink and downlink frames are transmittedat the same time over different carriers. TDD will in the future be usedfor most WiMAX deployments, since it allows for a more flexible sharingof bandwidth between up- and downlink, does not requires paired spectrumand has a reciprocal channel that can be exploited for spatialprocessing.

The downlink subframe 15 in TDD begins with overhead information forinforming the user device about the characteristics of the system. Theoverhead comprises synchronization information 17 and system information18. The overhead is followed by data regions 19 for the downlink datatraffic in the downlink subframe. A guard interval 20 is followed by anuplink subframe 21 with data regions for the uplink data traffic fromthe different user devices. Finally there is the end interval 22followed by the overhead synchronization information 17 of the nextframe.

In WiMAX particularly the overhead begins with a downlink preamble thatis used for physical-layer procedures (cell detection, time andfrequency synchronization). The preamble is followed by a frame controlheader providing frame configuration and system information (modulationand coding maps) to find where and how to decode downlink and uplink.The frame control header and maps are sent for each available dataregion 19, 22.

Uplink and downlink subframes can instead of TDD be divided withFrequency Division Duplex. FDD is more efficient in the case ofsymmetric traffic. Another advantage is that it makes radio planningeasier and more efficient. Compared with TDD, FDD divides the subframeby frequency instead, which means that the subframes are sent at thesame time using different frequencies.

In order to achieve high data throughput in cellular systems, high ordermodulation, e.g. 64 QAM and high transmit power is used at the basestation. The physical resources in term of subcarriers and time are keptto a minimum to maximize the user data throughput. High performancepower amplifier is needed to keep the signal prosperities after theamplification. Especially the linearity of the amplification isimportant. This requires a lot of energy which increases the energyconsumption of the base station. Due to these requirements the amplifierefficiency is low and contributes to a large extent the base stationpower consumption.

During low load or no load scenarios the base station still needs totransmit the system and synchronization information 17,18 to serve theattached mobiles and so a new mobile can access the system. Theinformation has to be transmitted with enough power to reach all mobileswithin the cell and is therefore transmitted with low modulation orderand high output power. Due to these transmissions the base station powerconsumption is still quite significant.

SUMMARY

The object of the present invention is to increase the energy efficiencyin a base station for a frame structure technology. The object is solvedby a method for energy saving in a telecommunication system according toclaim 1, a telecommunication system adapted for energy saving accordingto claim 14 and a node in said telecommunication system according toclaim 12.

The method according to the present invention relates to a method forenergy saving in a telecommunication system with at least one first basestation for enabling communication within the cell. A signal having aframe structure is transmitted and received in the cell by the firstbase station, the structure of the frame comprising a downlink framepart and an uplink frame part. Each frame part has the ability ofcarrying at least one data region allocated to at least one user orbroadcasted for the traffic flow between the telecommunication networkand the user terminal via the first base station. The downlink framepart comprises an overhead part with at least synchronization or systeminformation. The frame structured signal is transmitted periodicallywith a normal interval defined by the system. What particularlycharacterized the method is that the system during a power saving modeincreases the interval between at least a first and the next followingsecond frame structured signal to a power saving interval.

The node according to the present invention relates to a node in thetelecommunication system with at least one first base station forenabling communication within the cell. The system is adapted fortransmitting and receiving in the cell the signal with a framestructure, the structure of the frame comprising a downlink frame partand a following uplink frame part. Each frame part has the ability ofcarrying at least one data region allocated to at least one user orbroadcasted for the traffic flow between the telecommunication networkand the user terminal via the first base station. The downlink framepart comprising an overhead part with at least synchronization or systeminformation. The system is adapted for transmitting the frame structuredsignal periodically with a normal interval defined by the system. Whatparticularly characterizes the node is that it is adapted for increasingthe interval between at least a first and the next following secondframe structured signal during a power saving mode.

The system according to the present invention relates to atelecommunication system with at least one first base station forenabling communication within the cell. The system is adapted fortransmitting and receiving in the cell the signal with a framestructure, the structure of the frame comprising a downlink frame partand an uplink frame part. Each frame part has the ability of carrying atleast one data region allocated to at least one user or broadcasted forthe traffic flow between the telecommunication network and the userterminal via the first base station. The downlink frame part comprisingan overhead part with at least synchronization or system information.The system is adapted for transmitting the frame structured signalperiodically with a normal interval defined by the system. Whatparticularly characterizes the telecommunication system is that it isadapted for increasing the interval between at least a first and thenext following second frame structured signal during a power savingmode.

The advantage of the present invention is that by introducing a powersaving mode the base station power consumption is decreased with amethod that can easily be introduced in present and upcoming standards.

BRIEF DESCRIPTION OF DRAWINGS

In the following text the invention will be described in detail withreference to the attached drawings. These drawings are used forillustration only and do not in any way limit the scope of theinvention:

FIG. 1 shows a schematic view of the OFDMA frame structure.

FIG. 2 shows a more detailed schematic view for the OFDMA framestructure when operating in TDD mode.

FIG. 3 shows the signal transmission from the base station in low loadsituation with and without power saving mode.

DETAILED DESCRIPTION

The invention will now be described in detail with reference toembodiments described in the detailed description and shown in thedrawings. FIGS. 1 and 2 have already been described in relation toBackground above.

The embodiments refer to a method for energy saving in atelecommunication system. The telecommunication system and node isadapted for performing said method described herein.

The telecommunication system comprises at least one first base stationfor enabling communication within a cell. A base station communicateswith a mobile user terminal, such as a hand-held phone. In thetelecommunication system, the base station enables the communicationbetween one or more mobile telephones within a cell (a cell is ageographic area covered by the base station) and the base station.

A signal 23 having a frame structure is transmitted and received in thecell by the first base station, the structure of the frame comprising adownlink frame part 15 and an uplink frame part 16.

The embodiment shown in FIG. 2, which relates to TDD, comprises a framepart 15 in form of a subframe followed by a frame part 16 also in formof a subframe. The frame structure in TDD is divided into a downlinksubframe a following uplink subframe, a small guard interval 20 (seeFIG. 2) between the downlink and uplink subframe and an end interval 22(see FIG. 2) between the uplink and the downlink subframe of the nextframe. It should however be understood by the person skilled in the artthat the feature “frame part” as disclosed in the claims also includesembodiments with FDD, in which the frame parts are divided by frequencyinstead, or other technologies for duplex.

Each frame part has the ability of carrying at least one data regionallocated to at least one user or broadcasted for the traffic flowbetween the telecommunication network and the user terminal via thefirst base station. The fact that the allocated to at least one user orbroadcasted means that the invention includes both unicast traffic flowbetween the system and one user terminal, multicast between the systemand a group of user terminals and broadcast between the system and everyuser terminal within a broadcast domain.

The downlink frame part 15 comprises an overhead part 17, 18 with atleast synchronization or system information. Often both informationtypes 17, 18 are included but there is an option that only one of thesetypes is included in the overhead. Still, at least one of thesynchronization or system information has to be transmitted.Consequently, the term “or” will be used.

As described in connection with FIG. 2 the downlink frame part 15 beginswith overhead information for informing the user device about thecharacteristics of the system. The overhead comprises at leastsynchronization information 17 or system information 18. Thesynchronization information is used for time and frequencysynchronization between the first base station and the user terminal.

The system information contains modulation and coding scheme and mapswhich enables frame configuration between the first base station and theuser terminal. The overhead is followed by the data regions 19 for thedownlink data traffic in the downlink frame part 15, the uplink framepart 16 with data regions 21 for the uplink data traffic from thedifferent user terminals. As illustrated in FIG. 3 the data regions 19,21 may vary in size from one signal to the next, which is enabled forinstance with OFDMA.

FIG. 3 illustrates the fact that the frame structured signal 23, 24 istransmitted periodically with a normal interval defined by the system. Anormal interval in OFDMA is 5 ms. As shown there is a frame Frame Nfollowed by frames Frame N+1, Frame N+2, Frame N+3 and so forth.

The embodiment shown in FIG. 3, which also relates to TDD, comprises aframe part 15 in form of a subframe followed by a frame part 16 also inform of a subframe. It should however be understood by the personskilled in the art that the feature “frame part” as disclosed in theclaims also includes embodiments with FDD, in which the frame parts aredivided by frequency instead, or other technologies for duplex. In FDD,this means that the frame parts can instead be transmitted at the sametime.

The signal 23, 24 has to be transmitted periodically even if no dataregions 19, 21 are included. During low load or no load scenarios thefirst base station still needs to transmit at least the system orsynchronization information 17, 18 to serve the attached mobiles and soa new mobile can access the system. The information has to betransmitted with enough power to reach all mobiles within the cell andis therefore transmitted with low modulation order and high outputpower. Due to these transmissions the first base station powerconsumption is still quite significant.

The object of the present invention is to increase the energy efficiencyin a base station with a frame structure technology. The scope of thepresent invention is therefore, as described in the characterizingportion of the independent claims, that the system during a power savingmode increases the interval between at least a first 23 and the nextfollowing second frame structured signal 23 to a power saving interval.The second signal (se FIG. 23, lower part) is the next signal whichfollows immediately after the first signal. The overhead part iscontained in each transmitted signal and by increasing the interval tothe power saving interval power savings will be achieved.

The power saving interval is enabled by interrupting at least one thirdframe structured signal 24, see FIG. 3 lower part. This means that inorder to save energy at least one frame structured signal, named thethird signal, is interrupted. As an example the system may transmitthree signals 23 and thereafter interrupt ten signals 24. The threesignals in one row gives the user terminal time to decode theinformation in the overhead part 17, 18, such as UL map data, andprocess the information to be sent in the UL frame part 21.

The power saving interval is optionally enabled by interrupting theframe structured signal 24 periodically. The frame structured signal isfurther optionally interrupted by interrupting the overhead part 17, 18.For instance at least every second signal is interrupted. This is shownin FIG. 3 in the lower part where the interval is increased 3 times byinterrupting two signals Frame N+1 and Frame N+2. Since the overheadpart of Frame N+1 and Frame N+2 is transmitted with enough power toreach all mobiles within the cell such an interruption will save asignificant amount of energy.

The fact is also that the interrupted signals contains overhead parts17,18 which do not have to be sent later. Instead only the data regionor regions 19,21 of the interrupted signal are included in the frame ofthe next signal transmitted. This is shown in the signal 23 in Frame N+3(see lower part of the figure) where the data regions from Frame N+1 andFrame N+3 (see upper part of the figure) are included in the signal.

The power saving mode is activated by the system at certain operatingconditions such as the level of usage for the cell capacity, the numberof user terminals in the cell and/or statistics of cell usage over time.The intent of the present invention is to monitor the systemcontinuously and if the traffic load goes down for a period of time thepower saving mode may be activated. Using statistics of traffic loadover time will also be very useful. For instance it may be that anoperator has monitored a low traffic load in a certain cell at nightbetween midnight and 06.00 in the morning. The operator may then via amanagement system modify the operation of this base station so that thepower saving mode is activated every night between midnight and 06.00.The system may also be modified so that if the traffic load is below acertain level the power saving mode is activated. It is the operatorthat decides which quality of service that will be provided at certainconditions.

It is vital that the user terminal is aware of the power saving mode.Therefore, the overhead part of the transmitted frame structured signalsduring the power saving mode comprises information about the powersaving mode and its properties such as the power saving interval. Thepower saving interval can e.g. be given in a management message such asa downlink channel descriptor or as a value, or a code, in the map ineach transmitted frame.

The overhead part of the frame structure signal is transmitted withenough power to reach all user terminals within the cell wherein thedata region or regions are transmitted.

The power saving mode is controlled by an algorithm which is loaded intothe system in order to enable said method for energy saving.

The invention also relates to a node in the telecommunication systemwith at least one first base station for enabling communication withinthe cell. The system is adapted for transmitting and receiving in thecell the signal 23 with a frame structure, the structure of the frameFrame N, Frame N+1, Frame N+2, Frame N+3 comprising a downlink framepart 15 and a following uplink frame part 16. Each frame part has theability of carrying at least one data region 19, 21 allocated to atleast one user or broadcasted for the traffic flow between thetelecommunication network and the user terminal via the first basestation. The downlink frame part 16 comprising an overhead part 17, 18with at least synchronization or system information. The system isadapted for transmitting the frame structured signal periodically with anormal interval defined by the system.

What particularly characterizes the node is that it is adapted forincreasing the interval between at least a first 23 and the nextfollowing second frame structured signal 23 during a power saving mode.The system may comprise an algorithm which controls the power savingmode.

The present invention also relates to a telecommunication system with atleast one first base station for enabling communication within the cell.The system is adapted for transmitting and receiving in the cell thesignal 23 with a frame structure, the structure of the frame Frame N,Frame N+1, Frame N+2, Frame N+3 comprising a downlink frame part 15 andan uplink frame part 16. Each frame part has the ability of carrying atleast one data region 19,21 allocated to at least one user orbroadcasted for the traffic flow between the telecommunication networkand the user terminal via the first base station. The downlink framepart 16 comprising an overhead part 17, 18 with at least synchronizationor system information. The system is adapted for transmitting the framestructured signal periodically with a normal interval defined by thesystem.

What particularly characterizes the telecommunication system is that itis adapted for increasing the interval between at least a first 23 andthe next following second frame structured signal 23 during a powersaving mode. The system may comprise an algorithm which controls thepower saving mode.

The technology of the system is for instance WiMAX, LTE, UMTS or GSMwhich are all systems operating with frames/frame structure.Consequently, every system having frames as an overhead consuming alarge amount of energy relevant in relation to the present invention. Asan option the system operates with OFDMA for enabling multiple accesses.The system may use high order modulation scheme such as 64 QAM. Thealgorithm loaded into the system controls the power saving mode.

It will also be appreciated by the person skilled in the art thatvarious modifications may be made to the above-described embodimentswithout departing from the scope of the present invention. A possiblevariant is to just use the extended power saving interval for basestation downlink transmissions and scheduled uplink transmissions butkeep a standing allocation for random access attempts to reduce thelatency while in power saving mode.

1-18. (canceled)
 19. A method for energy saving in a telecommunicationsystem having at least one first base station for enabling communicationwithin a cell, a signal having a frame structure being transmitted andreceived in the cell by the first base station, the structure of theframe comprising a downlink frame part and an uplink frame part, eachframe part having the ability of carrying at least one data regionallocated to at least one user or broadcasted for the traffic flowbetween the telecommunication network and the user terminal via thefirst base station, the downlink frame part having an overhead part withat least synchronization or system information, the frame structuredsignal being transmitted periodically (Frame N, Frame N+1, Frame N+2,Frame N+3) with a normal interval defined by the system, the methodcomprising the step of: increasing, by the telecommunication systemduring a power saving mode, the interval between at least a first andthe next following second frame structured signal to a power savinginterval.
 20. The method according to claim 19, wherein the normalinterval is 5 ms.
 21. The method according to claim 19, wherein theoverhead part is contained in each transmitted signal.
 22. The methodaccording to claim 19, further comprising the step of enabling the powersaving mode by interrupting at least one third frame structured signal.23. The method according to claim 22, further comprising the step ofperiodically interrupting the frame structured signal.
 24. The methodaccording to claim 22, wherein at least every second signal isinterrupted.
 25. The method according to claim 22, further comprisingthe step of including at least the data region or regions of theinterrupted signal in the frame of the next signal transmitted.
 26. Themethod according to claim 22, further comprising the step ofinterrupting the overhead part of the frame structured signal.
 27. Themethod according to claim 19, further comprising the step of activatingthe power saving mode at certain operating conditions, such operatingconditions being selected from the group consisting of the level ofusage for the cell capacity, the number of user terminals in the celland statistics of cell usage over time.
 28. The method according toclaim 19, further comprising the step of including in the overhead partof the transmitted frame structured signal during the power saving mode,information about the power saving mode and its properties such as thepower saving interval.
 29. The method according to claim 19, wherein theoverhead part of the frame structure signal is transmitted with enoughpower to reach all user terminals within the cell wherein the dataregion or regions are transmitted.
 30. The method according to claim 19,wherein the power saving mode is controlled by an algorithm.
 31. A nodein a telecommunication system with at least one first base station forenabling communication within a cell, the system configured to transmitand receive in the cell a signal with a frame structure, the structureof the frame comprising a downlink frame part and an uplink frame part,each frame part carrying at least one data region allocated to at leastone user or broadcasted for the traffic flow between thetelecommunication network and the user terminal via the first basestation, the downlink frame part having an overhead part with at leastsynchronization or system information, the system being configured totransmit the frame structured signal periodically (Frame N, Frame N+1,Frame N+2, Frame N+3) with a normal interval defined by the system, thenode comprising: means for controlling an increase of the intervalbetween at least a first and the next following second frame structuredsignal during a power saving mode to a power saving interval.
 32. Thenode according to claim 31, wherein the node comprises a computerimplemented algorithm embodied on a non-transitory computer readablemedium configured to cause a processor to control the power saving mode.33. A telecommunication system with at least one first base station forenabling communication within a cell, the telecommunication systemconfigure to transmit and receive in the cell a signal with a framestructure, the structure of the frame comprising a downlink frame partand an uplink frame part, each frame part having the ability of carryingat least one data region allocated to at least one user or broadcastedfor the traffic flow between the telecommunication network and the userterminal via the first base station, the downlink frame part having anoverhead part with at least synchronization or system information, thetelecommunication system configured to transmit the frame structuredsignal periodically (Frame N, Frame N+1, Frame N+2, Frame N+3) with anormal interval defined by the system, the telecommunication systemcomprising: a processor within a node configured to increase theinterval between at least a first and the next following second framestructured signal during a power saving mode to a power saving interval.34. The telecommunication system according to claim 33, wherein thetelecommunication system operates according to a standards specificationselected from the group consisting of WiMAX, Long Term Evolution (LTE),Universal Mobile Telecommunications System (UMTS) and Global System forMobile Communications (GSM).
 35. The telecommunication system accordingto claim 33, wherein the system enables multiple accesses usingorthogonal frequency division multiple access (OFDMA).
 36. Thetelecommunication system according to claim 33, wherein the systemcomprises an algorithm controlling the power saving mode.